TO SAY THAT “The Simpsons Movie” has been a long time coming is like saying Homer is a bit full-figured

or principal Skinner has a few mommy issues. Severe understatement.

In the years between when the film was first proposed and when it finally made it to the big screen, baby Maggie could have grown nearly old enough to get legally Duff-faced at Moe’s.

The film finally – finally – hits screens Friday, but its genesis actually goes back to the early days of the series, which enters its 19th season this fall and is celebrating 20 years since it debuted on “The Tracey Ullman Show” in 1987.

“When I heard they were making a movie, I felt like a lot of people. I thought, what took them so long?” says Joe Mantegna, who voices gangster “Fat Tony” in the movie and TV series. “I was surprised they hadn’t done one sooner, because they’ve made movies of lesser things a lot sooner. I kept hearing, ‘It’s coming out

next month, next week, next year.’ There’s been a buzz about it for a long time.”

Assembling the resources for a full-length feature proved to be the holdup.

“In the early years of the show, a movie was talked about in an offhand way. Really, we didn’t have enough writers and directors to do a show and the film simultaneously. We only had eight writers and five directors,” says Al Jean, one of the film’s writers, who’s been with the series since its beginning.

“We were all busy on the show,” says writer David Mirkin, who joined the show in its fifth season. “It takes a year and a half to do one season of the show. It takes nine months to do one episode. We’re literally working on two seasons at once, with no time off.

There always were just a handful of people who really knew how to write the show, and there were never enough of us to peel off and do the film.”

Then, six years ago, the pieces – and more important, the legal contracts – to get a movie made fell into

place.

“We accumulated more [staff] over the years, and in 2001, when the cast signed a deal to do the new seasons,

they also signed a deal to do a film,” Jean says.

With the cast in place, series executive producer and guiding force James L. Brooks – a veteran of “The

Mary Tyler Moore Show” and “Taxi” – began assembling writers to hammer out the script. And those he picked have fans – even lapsed ones who haven’t watched the show in a few seasons – as excited as Ralph

Wiggum after 11 Pixy Stix.

“When Jim finally decided [to move forward with the film], he chose the classic writers, the show runners, and that’s how the team came to be. It was Jim’s vision that it be this group who are considered the key Writers,” Mirkin says.

If you’ve been watching the show for any length of time, the names should be familiar. In addition to Jean and Mirkin, Brooks tapped John Swartzwelder (who holds the writing record for most episodes of the series at nearly 60), Ian Maxtone- Graham, George Meyer, Mike Reiss, Mike Scully, Matt Selman and Jon Vitti.

The group commenced writing in November 2003 – and alarmingly enough, were making changes up until just a few weeks ago. The script went through at least 100 revisions over the years. Scenes, even those that had been fully animated, were cut and reworked, and Jean estimates that enough for an entire film was left

on the cutting-room floor. Look for some of it on the DVD.

But the forces behind the film are adamant that you shouldn’t wait for the DVD. They insist “The Simpsons Movie” is a cinematic experience that differs from the TV show.

“We’re trying to tell a story that’s emotionally involving for 90 minutes, that compels you to not just sit there and laugh, but to care about what happens for the full length of a movie – as they do in a Pixar film or a great Disney film,” Jean says. “It’s also in wide-screen format. We tried to be more ambitious in the directing, in the use of color and shadow.”

Plus, you reportedly get to see Bart’s wee-wee. “I can’t confirm or deny that,” says Nancy Cartwright, who voices the oldest Simpson child.

There’s not much else anyone can confirm or deny about the movie, because the producers have been incredibly secretive about plot details, giving guest stars only their relevant script pages (with the star’s name plastered on every page, to prevent leaking) and booking recording sessions under a fake movie title.

What we do know is that the plot centers around Homer’s biggest d’oh moment yet. He poisons Springfield with a silo full of pig droppings, incurring the wrath of his family, the town – and president Arnold Schwarzenegger. Yep.

“I think the movie will be successful. It’ll be interesting to see,” says Albert Brooks, who has done frequent guest voices over the years and has a role in the movie. “I think if they can pull this off, it’ll be considered an amazing achievement. There’s all these people with preconceived notions of, oh, what’s it gonna be? Is it too

late? Is it the right time? You’re getting a lot of people walking in with something they think they should be seeing.

“Listen, that’s one of the pitfalls of being the most successful animated series in the history of the world.”